The Principle of Evidentialism states that a Subject is justified in believing p if the belief is proportioned according to evidence at a given time. That is, S is epistemically justified in believing a proposition at time t if and only if the belief is supported by S’s evidence at time t.
Suppose I maintain the belief that I will pass all my philosophy classes. The evidence I have for this belief is that I have received all passing grades through the semester, that there are no new assignments, there is no class curve, and it is now the last day of classes. I am justified in believing that I will pass because all the evidence supports this belief; namely that all my grades are undeniably above passing and there are no more opportunities to earn credit toward my grade.
This belief is justified because the proposition “I believe that I will pass all my philosophy classes” is supported evidence “it has been confirmed that all the grades I received in all these classes are undeniably passing” at the time the proposition was stated, i.e. at the last day of classes. It is important that all evidence is properly accounted for, including knowledge of a class curve and the relation of these grades to other students. Also vitally important is that the proposition is stated according to the evidence at time t. If it was stated earlier there would be insufficient evidence to uphold that belief because not all possible grades were completed.